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#2417308 - 10/26/11 07:50 PM 1998 z71 front &rear diff's
Jaybird79 Offline


Registered: 11/01/10
Posts: 7
Loc: Illinois
Hi does anybody know if i can run Mobil 1 75w90 in both the front and rear differentials in this truck? Also do i need to put any LS additive in either one,it does have the Eaton G80 in the rear.

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#2418125 - 10/27/11 05:45 PM Re: 1998 z71 front &rear diff's [Re: Jaybird79]
artificialist Offline


Registered: 09/23/07
Posts: 6899
Loc: Florida
What does your owner's manual say your truck needs?
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#2418283 - 10/27/11 08:40 PM Re: 1998 z71 front &rear diff's [Re: Jaybird79]
Fazzone Offline


Registered: 08/17/09
Posts: 104
Loc: Mondovi Wisconsin
Yes, you should be fine. I had no issues in my last truck('98 GMC 1500 Z71) running it. As far as the LS additive, mine didn't need it, but I don't recall specifically which rear end was in it. The manual specs call for conventional in the front, but if you want to spend the extra $ go for it.
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#2418285 - 10/27/11 08:40 PM Re: 1998 z71 front &rear diff's [Re: Jaybird79]
Jaybird79 Offline


Registered: 11/01/10
Posts: 7
Loc: Illinois
SAE 80w90 GL-5 gear oil front and rear.

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#2418463 - 10/28/11 05:55 AM Re: 1998 z71 front &rear diff's [Re: Jaybird79]
NHHEMI Offline


Registered: 07/06/07
Posts: 5136
Loc: NH
Originally Posted By: Jaybird79
Hi does anybody know if i can run Mobil 1 75w90 in both the front and rear differentials in this truck? Also do i need to put any LS additive in either one,it does have the Eaton G80 in the rear.


You can run 75W90 synthetic in both and it would be an upgrade. No LS additive required with the G80 but if the fluid you select has it don't worry. It will still work fine.
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#2418503 - 10/28/11 07:49 AM Re: 1998 z71 front &rear diff's [Re: Jaybird79]
Jaybird79 Offline


Registered: 11/01/10
Posts: 7
Loc: Illinois
Thanks NHHEMI, just wanted make sure it would be okay. I can get the mobil 1 for about $4.00 a qt at AAP so I thought why not upgrade.

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#2419234 - 10/28/11 09:25 PM Re: 1998 z71 front &rear diff's [Re: Jaybird79]
wtd Offline


Registered: 06/25/02
Posts: 1177
Loc: southwest Mo.
I run shell coventional 80W-90 gear oil in my 98 Z71 but used to run Mobil 1 in both diffs. It might just be a coincidence but I had to have my rear end rebuilt at 75,000 miles with hardly any towing or hauling. After that I went back to conventional and now at 120,000 miles, no problems. I first started hearing noises at about 55,000 miles but could not figure out what it was and finally had it looked at professionally which ended up with the repair. Others have had good luck with it so for that price you might as well try it.

Wayne
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